1. Field of the Invention
The invention relates generally to disk drive control structures and techniques and in particular relates to improved methods and structures for measuring digital sampled values from a read channel of a digital communication channel (such as a disk drive read channel) to measure various operational parameters of the read channel. The methods and structures generally include flexible programmable structures for selectively accumulating digital sampled values during operation of the read channel.
2. Discussion of Related Art
Present-day storage systems and other data storage or communication applications, sense recorded or transmitted data encoded as digital information. The encoded digital information is stored or transmitted as analog pulse signals stored on a recording surface or transmitted through a communication medium. The pulses are demodulated and decoded to reproduce the stored or communicated information. Typically, such a digital communication channel includes a read channel component used for receiving the analog pulse waveforms, for converting the analog information to discrete time sampled digital values, and for decoding the original stored or communicated data from the discrete time sample values. In general, such a read channel therefore generally includes an analog to digital converter component for generating a sequence of discrete time sample values and includes digital decoding logic for detecting data or information derived from the digital discrete time sampled values.
Numerous analog filter structures and digital filter structures may be included through the communication paths representing the read channel to improve quality of the signal processing and the data decoding processing features. A process of decoding the digital information from discrete time sampled signals typically entails discrete Fourrier transforms to extract and isolate numerous superposed signals including the desired data signal as well as harmonics and noise caused by various mechanical and electrical characteristics of the system applying the read channel.
Due to the analog nature of the underlying modulated signal, it is frequently useful to adjust or tune various filters in the read channel operation to optimize the quality of signal demodulation and decoding. In performing such optimizations, is often useful to filter out harmonic signals using discrete Fourrier transforms and to identify other operational parameters associated with the read channel operation. Measurements useful for these optimizations may be obtained utilizing external analyzers such as spectrum analyzers to determine the spectral content of the underlying modulate it signal. Obtaining and utilizing an external spectrum analyzer for such purposes is both inconvenient and costly. Using an external analyzer is inconvenient in that an external device must be utilized and in some manner coupled to the underlying system without itself impeding or altering operation of the underlying system. Further, such devices are often extremely costly such that evaluating and optimizing multiple read channel devices simultaneously, such as in a manufacturing test and calibration environment, can be a can represent a significant cost.
One prior solution taught by Baker proposes a device referred to as a harmonic sensor. The harmonic sensor structure of Baker receives the sequence of digital, discrete sampled values in a circuit integrated with, or tightly coupled with the read channel logic and is adapted to accumulate the discrete signal samples at predetermined intervals to thereby determine harmonic signal aspects of the sensed information. In this Baker solution, the modified read channel circuit is used to perform spectral analysis to identify harmonics within the sampled signal. Though the Baker solution provides some capabilities for integrated spectral analysis within the read channel circuit, the solution is limited in terms of its flexibility and potential measurements.
It is evident from the above discussion that an ongoing need exists for improved spectral analysis features integrated within, or tightly coupled to, read channel circuitry in a digital communication system.